Well, I got a reply so that's something.
Apparently if you create a listing from a template that doesn't already have international shipping you now can't add a rate table to the new listing. Helpful.
There is apparently no way to add an international rate table to an existing listing.
I tried creating a new listing and couldn't add the international rate table in that either.
The only way I could add my rate table was to put in a flat European rate (which is in my rate table anyway), and then it would allow me to add the rate table. What a faff.
It seems to me that eBay are trying to make international shipping so difficult that you give up and use GSP. Well I refuse to use GSP. I've been shipping items overseas all by myself since before GSP existed and I don't need it now.